Magnetic material



Aug. 11, 1931. w ELMEN 1,818,054

MAGNETIC MATERIAL Original Filed Jan. 12. 192'? FIG! RESISTIVITY IN MICROHM- CMS PERCENT SILICON L l I l I l J l l l .2 .4 .6 .8 1.0 1.2 1.4 L6 L8 2.0 2.2 2.4 2.6 2.8

FIG. 2

. INITIAL PERM EABILI'VTY 'PERCENT SILICON I I l l .2 .4 .6 .8 L0 L2 L4 L6 L8 2.0 2.2 2.4 2.6 2.6

FIG. 3

//v VENTOR .G. W. ELME N A TTORNEV Patented Aug, 11, 1931 UNITED STATES PATENT oF c-E GUSTAF W. ELHEN, OF LEONIA, NEW JERSEY, ASSIGNOR TO WESTERN NLECTRIG COH- PANY, INCOREORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK MAGNETIC MATERIAL Original application filed January 12, 1927, Serial No. 160,569. Divided and this application filed June 20,

. 1930. Serial No. 462,558.

meability, especially at low magnetizing.

forces, and high resistivity with consequent low eddy current losses.

Magnetic materials have been variously employed in electrical systems for such pur-' poses as the cores of loading coils, trans formers, magnetic modulators and the like, for tractive electromagnets, dynamos, motors, telephone receivers, telegraph relays, etc. Magnetic materials have also been employed for the continuous loading of signal ing conductors, but until recentl their use has been limited to relatively s ort cables for telephone purposes. Heretofore, the magnetic materials generally used for these purposes have been soft iron and silicon steel. The principal possible rivals of iron are nickel andcobalt but they are far below iron in permeability at the magnetizing forces involved in such apparatus. With nickel and cobalt in this respect, stands Heuslers alloy of aluminium, manganese, and copper. It has been-found that a composition of about nickel and 4), copper, when tested at low magnetizing forces, gives a permeability higher than that of iron alone. It will be seen that with the exception of aluminum, all these metals stand close together in their atomic weights and atomic numbers, and in this specification the five elements, manganese, iron, cobalt, nickel and copper, having the consecutive atomic numbers 25, 26, 27, 28 and 29, will be referred to as constituting the magnetic group of elements.

Recently, alloys .comprising elements of the magnetic group and especially those consisting chiefly of nickel and iron, have been employed to great advantage particularly ,in connection with signaling systems and apparatus in which the magnetic forces 1nvolved seldom exceed .2 gauss. Such alloys and the method of producing them are disclosed in United States Patent No. 1,586,884, granted to G. W. Elmen, June 1, 1926, and in application Serial No. 48,188 referred to above.

That application discloses a composition comprising elements of the so-called magnetic group with the addition of a third element and having high permeability and resistivity, and small hysteresis and eddy current losses. Amon the compositions mentioned is an alloy 0% nickel, iron and silicon.

Thepresent invention relates to magnetic alloys consisting of at least two elements of the magnetic group combined in suitable proportions with silicon. These alloys, when subjected to a proper heat treatment and guarded against undue stresses and other disturbing causes, not only develop and retain an extremely high-permeability at low magnetizing forces of the order of .2 gauss or less,but at the same time have a notably high resistivity and consequent low eddy current loss. Furthermore, they can be applied with advantage to the continuous loading of signaling conductors in such a manner as to obtain the full benefit of the above noted desirable properties.

In its preferred form the alloy of the present invention comprises nickel, iron and silicon properly proportioned and properly heat treated as described in the following detailed description in connection with the drawings in which: I

Fig. 1 shows graphically the relation between the resistivity and the percentage of silicon in alloys comprisin nickel, iron and silicon, the proportions o nickel and iron being approximately in the ratio of 78 to 22- 7 Fig. 2 shows graphically the general trend of the initial permeability with respect to the percentage of silicon of the same al loys; and

Fig. 3 shows a signaling conductor loaded with the magnetic material of this invention in the form of ta The curve of Flg. 1 shows that the resistivity of alloys containin as the basic constituents about 78% nic el and 22% iron may be increased by the addition of small amounts of silicon. The high resistivity of these allo s makes them particularly well adapted or use where low eddy current losses are desirable.

The curve 'of Fig. 2 shows the general trend of the initial permeability of this group of alloys with respect to the percentage of silicon. The sam les upon which this curve is based were sub ected to the double heat treatment hereinafter described. As shown by this curve,fsilicon in percentages up to about 1% has little effect on the init1al permeability, while larger quantities tend to decrease the initial permeability. The hi resistivity together with the relatively h initial rmeability of these alloys ren ers them fitter than iron for use as a loading material for signaling conducaa tors, and for other uses where the magnetizof silicon below a for a sample alloy containing about 0.51% silicon it was found that the strengths of ing forces are small and low eddy current losses are desirable, as in transformer and inductance coil cores.

The magnetization curves for this group of allo s nerally follow the characteristics o t nickel-iron alloy containing 78 nickel and 21%% iron as shown in a p 'cation Serial No. 48,188 referred to vs. The additionof silicon in increasing amounts causes the curve to rise 1cm rapidly at the origin and reach a saturation point at a lower magnetizigg force, although the effect is not re mark for percentages ut 1%. For example,

the magnetic fields for magnetizing forces of 0.05, 0.1, 02, 0.5, 1.0, 2.0, 5.0 and 10.0 gauss were 1,850, 5,680, 6,720, 8,540, 9,350, 9,810, 10,250 and 10,400 gauss, respectively. Althou h alloys of this group containing at least 0% mckel and preferably about 78% nickel have been found to give the highest permeability and to be preferable for many urposes, these characteristics are not limi to these particular rcen of=;nickel, since, by decreasin t e quantity of nickel in the material, a oys having a higher resistivity may be obtainedi although the initial permeability of such al oys is or: dinarily decreased by the use of smaller quantities of nickel. Any quantity of nickel in the alloy greater than 25% to which will ve a considerably hi her initial rmeahilit than iron, may employe in iron-nic el-silicon compositions in accord ance'with this invention. For many purposes in which low eddy current loss is a rime requisite, as is the case for cores for lbading coils and for loading material for above, to a tempo signaling conductors, an alloy of a lower percentage of nickel, or a higher percenta of silicon, or both, me be found preferab e to the alloys having 'gher initial permeability but lower resistivity.

In preparing magnetic materials according to this invention, nickel, iron and silicon in the desired proportions are fused together in an induction furnace and then poured into molds and formed or worked into the desired shape. For continuously loaded conductors a particularly suitable form for the allo is that of a tape about .006 inch thick an about .125 inch in width.

In order to give the alloy the desired characteristic it is necessary to subject it to a process of heat treatment which will depend u on the composition of the allo and upon t e articular characteristics WlllCll it is desira Is to roduce in the material. An example of t is heat treatment is the heating of the alloy to about 1100 C. and maintaining it at that temperature for a period of approximately one hour and subsequently cooling the material slowly. The rate of cooling and temperature to which the material is heated may be determined by ex riment in each case, in order that those c aracteristics sought 1n the articular material may be produced to the ired degree. An avera e rate of cooling which has been .foun to be suitable is approximately 5 0.

per minute. The temperature to which the material is heated may vary considerably from the above value. For materials containing hi her errzentages of silicon it may be desirab e to eat the material to a somewhat higher temperature.

For a oys containing various rcentages of silicon 1t has in general been ound preferable to employ a modification of this heat treatment in which the alloy is reheated after the initial heat treatment, outlined rature somewhat above its magnetic transition point. The material is then cooled to room temperature, past the magnetic transition point at a certain rate which should be determined for each alloy, but which is preferably faster than that employed in an anneal, but not so fast as to set up strains in the material due to uneven cooling throughout the body.

A modified form of heat treatment which may be desirable in some instances is to omit the reheating rocess and cool the material from the original annealingtemperature in two steps; cooling to a point slightly above the magnetic transition point being carried on at one rate, and from that pointto room tem erature at a more rapid rate.

i hen the material is to be used for the continuous loading of signaling conductors, it is formed into a. ta having substantially the dimensions sta above. This tape is produced by. working the alloy into the form of a rod or bar by repeated steps of swaging and annealing. The bar is subsequently drawn down to the form of a wire of about No. 20 B.- & S. gauge and then passed between rollers whereby it is flattened into tape of the proper thickness. This tape is then passed between cutting rolls or discs which trim its edges squarely at both sides and give the tape uniform width.

The loaded conductor shown in Fig. 3 comprises a stranded core consisting of a central cylindrical wire 11 enveloped by a plurality of surrounds 12 which are shaped to fit together closely to form a cylindrical annulus about the central wire. The magnetic. material 13 in the form of tape is wrapped helically about the stranded core, as disclosed in U. S. Patent No. 1,586,887, granted to G. W. Elmen, June 1, 1926.

.When it is desired to use a loadin material in the form of a Wire 'rather t an a tape the drawing processes as outlined above are continued until the wire has the desired dimensions.

, After ,the loading tape has been applied to the core, it is given its final heat treatment by drawing the assembled loaded conthe type described in U. S. Patent No. 1,586,884 referred to above. This is an electric furnace of the mufile type having a horizontal iron heating tube extending through the furnace and projecting a. considerable distance beyond. The furnace is maintained at the optimum temperaturev for the particular composition of the alloy being employed. The length of the pass through the 0.3% to 5% of silicon, and the remainder iron.

3. A magnetic material which comprises as an essential component a composition containing 33% to 48% of nickel, 0.3% to 5% of'silicon and the remainder iron, such composition havin high initial. permeability and high speci c resistance.

4. An alloy of nickel, .iron and silicon, heat treated to develop therein high permeability for magnetizing forces of the order of 0.2 gauss and less, said alloy comprising 0.2% to 3% silicon, 33% to 50% nlckel and the balance iron.

In witness whereof, I hereunto subscribe 80 my name this 19th day of June, 1930.

. GUSTAF W. ELMEN.

ductor through a furnace, for example of heating tube and the rate at which the conductor is moved are chosen so as to produce the most desirable magnetic characteristlcs in the loaded conductor. After cooling the conductor is insulated and formed into a cable in the usual manner.

It will be found that certain of these alloys are better suited for some. particular uses than others, and that the characteristics of any alloy may be varied by the use of different heat treatments. No attempt has, therefore, been made to give an exhaustive analysis of the characteristics of each composition but merely to point out gen- Illli 

